Photo-chemical printing process and sheet material



Dec. 31, 1963 R. E. MILLER 3,116,148

PHOTO-CHEMICAL PRINTING PROCESS AND SHEET MATERIAL Filed D60. 21, 1959 COATING OF MINUTE PRESSURE- RUPTURABLE CAPSULES EACH CONTAINING LIQUID SOLVENT FOR PHOTO-SENSITIVE DYE FORMER COMPOUND INTERSPERSED AMONG THE CAPSULES IN SOLID PARTICULATE FORM IN WHICH FORM IT IS INSENSITIVE TO ULTRA-VIOLET LIGHT CAPSULES RUPTURED ACCORDING TO IMAGE TO BE RECORDED, GIVING A LATENT IMAGE AS A LOCALIZED COLORLESS LIQUID DYE FORMER SOLUTION WHICH CAN BE DEVELOPED BY EXPOSURE TO ULTRAVIOLET LIGHT TO A COLORED STATE LATENT IMAGE DEVELOPED BY EgggSURE To ULTRA-VIOLET IF DESIRED,COATED SHEET WITH H6 4 DEVELOPED COLORED IMAGE MAY BE PASSED THROUGH CALENDER ROLLERS CALENDER ROLLS TO RUPTURE ALL UNRUPTURED CAPSULES, LEAVING SHEET INSENSITIVE To FURTHER COLORED IMAGE-BEARING IMAGE-PROVOKING ACTION COATING INVENTOR ROBERT E. MILLER BY -44! W n HIS ATTORNEYS United States Patent Ofiice 3,13 ind i3 Patented Dec. 31, 1963 3,116,143 PHOT=CHEMHCAL PRINTING PROCESS AND SHEET MATERHAL Robert E. Miller, Dayton, @hio, assignor to The National (lash Register (loinpany, Dayton, Ohio, a corporation oi Maryland Filed Dec. 21, 1959, Ser. No. 861%,787 11 Claims. (6i. 964-8) This invention relates to a photo-chemical printing process and sheet material and more particularly relates to such a process employing a base-Web film-like sheet having thereon a coating of a profusion of minute solid particles of colorless dye former material that in liquid solution becomes readily responsive to ultra-violet light by becoming colored, and becomes fixed in the colored state when the solvent evaporates, said particles of dye former material having interspersed therebetween a profusion of minute liquid-solvent-containing rupturable capsules, said capsules, if desired, having gas-producing substances in the capsule material. The sheet without the gas-producing substances in the capsules is disclosed in an application for United States patent, erial No. 694,802, filed by Elliot Berman on November 6, 1957, now United States Patent No. 3,090,687. That application discloses a sheet and process in which the sheet, prior to being subjected to ultra-violet light, has had all the capsules on the sheet crushed, rendering the whole sheet sensitive to ultra-violet light regardless of the image to be made thereon, and the image is made by projecting ultra-violet light through a stencil to form the image in color.

In the process of this invention, capsules containing iquid solvent are used interspersed with particles of such dye former material, so that, when the capsules are ruptured, a photo-responsive liquid solution is formed, but only those capsules are ruptured that are in the area circumscribed by the desired image borders, and this can be accomplished by blow, pressure, or heat, as will be described, to form such colorless liquid dye former solution that can be developed into a colored image by ultraviolet light applied to the entire sheet. The areas in which the capsules remain unruptured are not colored. The colored image is fixed if an evaporable solvent is used and is allowed to evaporate, leaving the colored form of the dye in solid form. Before such resolidification of the dye, the liquid image in color may be erased by heat or by being subjected to light in the green through ultraviolet region of the spectrum.

To further render the colored-image-bearing sheet insensitive after the image is fixed, all the unruptured capsules may be ruptured by passing the sheet through calender rolls and allowing the escaped solvent to evaporate in the absence of predominatingly ultra-violet light.

Therefore, the invention provides a novel process, and sheet for use therewith, for producing colored images photo-chemically, and the process, in its various aspects, will be described with reference to the drawing, of which:

FIG. 1 is a diagrammatic perspective view of a sensitized sheet used in the process, with suitable descriptive legends which also accompany the other views;

FIG. 2 is a diagrammatic perspective view of the sheet showing, in phantom, the outlines of an area in which the image exists in latent, colorless, form as a liquid solution of the dye former particles caused by local rupture of the capsules;

FIG. 3 is a diagrammatic perspective view of the sheet of FIG. 2, With the image having been developed to a colored form by the application of ultra-violet light to the whole sheet; and

FIG. 4 is a diagrammatic view of how the sheet of FIG. 3 is rendered insensitive to produce any more images, by being passed between calender rolls to crush any unruptured capsules, which is an optional step following the main process steps.

General Description The coated sheet shown in FIG. 1 may be constructed in the manner shown in application for United States Letters Patent Serial No. 694,802, now United States Patent No. 3,090,687, which has been mentioned. A record material base Web sheet, preferably fibrous paper or polymer film, is coated with a liquid suspension of micro-fine colorless solid dye former particles which are immiscible with the liquid suspension vehicle, which sus pension vehicle in the preferred form of the invention is Water and the dye former a water-immiscible material, interspersed with minute rupturable microscopic capsules each having within it a volatile colorless liquid solvent for the dye former particles. The capsules and the dye former particles should be small enough that they may not be individually resolved by the unaided eye.

As a particular embodiment, cc. of polyethyl benzene is emulsified in grams of an 11 percent, by weight, aqueous solution of gelatin, said solution having been adjusted to a pH of 5.5-5.6, if not already at such pH due to the method by which the gelatin was manufactured, the emulsification being carried on at 55 degrees centigrade until the drop size is 5 microns or less. To this emulsion is added 180 grams of an 11 percent, by weight, aqueous solution of gum arabic, and, while the SS-degree-centigrade temperature is maintained, with constant agitation, Water is introduced to make a total volume of 1800 cc. of material. With continued agitation, the pH of the system is lowered to about 4.5 to cause a phase separation of the gelatin and the gum arabic as a rich sol of complex entities which deposits, collects, and coalesces around each drop of the dispersed polyethyl benzene as liquid walls, which are set to a firm. but pressure-rupturable condition by cooling, the pressure-rupturable walls confining the polyethyl benzene keeping it from being dissipated by evaporation until its release is desired. The hot system of liquid-walled capsules in the, now, polymer-poor aqueous vehicle is cooled, with continued agitation, to 14 degrees centigrade over a period of fifteen minutes to set the capsule walls to the firm rupturable state. To harden the capsule walls, there is added to the system 10 cc. of a 25 percent, by weight, aqueous solution of glutaraldehyde, which cross links the gelatin of the capsule walls, in a manner well known. The capsules are recovered from the residual aqueous vehicle, containing undeposited polymer material and unreacted glutaraldehyde, by filtering or other convenient method, and are redispersed in an aqueous dispersion of solid particles of the photo-responsive dye former, so that the solids content thereof is approximately 15 percent, by weight, there being 10 parts of capsules to one part of dye former particles, by weight, therein, although the solids content may be varied considerably from these amounts given as preferable, as the water of the dispersion merely acts as a convenient means for facilitating the coating of the dispersion onto the supporting web. The coating, if applied to paper with ordinary absorbency to printing links, should be so applied that in the dry coated form it will weigh about six pounds per ream of sheets 25 inches by 38 inches.

Among the best colorless dye formers that in liquid solution in a solvent like polyethyl benzene, which is not so volatile that it will evaporate before an operator can subject the liquid latent image to ultra-violet light, are the 6-nitro and the S-chloro, 6'-nitro derivatives of the parent compound 1,3,3-trimethyl-spiro (2" -1-benzopyran-2,2'-indoline), which has the structure and the above-mentioned derivatives of which, in liquid solution, turn dark blue when subjected to ultra-violet light. Many other derivatives of this parent compound that function in the same manner are disclosed in application for United States Letters Patent Serial No. 803,836, filed by Elliot Berman on April 3, 1959.

Generally, aromatic hydrocarbon solvents may be used, and such may be selected for their solubility and evaporation characteristics.

Other dye formers than the derivatives of the parent compound specifically named, and those disclosed in said application Serial No. 803,836, may be found in applications for United States Letters Patent Serial No. 821,3 83, filed June 19, 1959, by Elliot Berman and David B. Mc- Quain, now United States Patent No. 2,978,462, issued April 4, 1961; Serial No. 827,175, filed July 15, 1959, by Elliot Berman and David B. McQuain, now United States Patent No. 3,022,318, issued February 20, 1962; Serial No. 827,462, filed July 16, 1959, by Elliot Berman and John E. G. Taylor; Serial No. 827,463, filed July 16, 1959, by Elliot Berman and David B. McQuain; and Serial No. 827,719, filed July 17, 1959, by Elliot Berman and David B. McQuain.

The record material which has been described may have the capsules in the coating ruptured by pressure such as that produced by the impact of letter-press type, by stylus, or by a squeeze impression by dies or rollers, or by heat if the capsules have in them a heat-responsive gas-producing material, in which case the rupture of the capsules is brought about by a heated stylus or type, or by heat rays projected through a stencil onto the record material in the configuration of the desired image. In the form of the invention in which the capsules are supplied with a gas-forming material, the gas-forming material may be present either in the nucleus liquid contents of the capsules or in the walls thereof. Such sheet material having solvent-containing minute capsules thereon is disclosed in an application for United States Letters Patent, Serial No. 769,058, filed on October 23, 1958, by Herman I. Eichel, the solvents in that application being toluene, kerosene, light petroleum fractions, and xylene, which all are evaporable and able to dissolve the photoresponsive colorless dye formers which have been specified. However, in said application the solvent is used to dissolve a particulate solid non-tacky adhesive interspersed among the capsules, such adhesives being made tacky upon the rupture of adjacent capsules by applied heat. The heat-responsive record material sheet used herein is a difierent structure from that disclosed in said Eichel United States patent application, inasmuch as the dissolvable material is a photo-responsive dye former and not an adhesive, thus forming a new combination of elements which may be used to obtained printed images.

As a first example of heat-rupturable liquid-solventcontaining capsules having solid walls, there will be disclosed the method of suspending the gas-producing substance in the encapsulated nucleus liquid solvent. Three parts, by weight, of the gas-producing material p,p'-oxybis-(benzenesulfonyl hydrazide), which is sold commercially, at present, by Naugatuck Chemical Division of United States Rubber Company, of Naugatuck, Connecticut, under the trade name Celogen, and which is a solid, the molecules of which individually decompose at a temperature of 266 degrees Fahrenheit upward, as a gas, is dispersed in 17 parts, by weight, of polyethyl benzene to form an internal phase which is emulsified in 29 parts, by weight, of a 3.5 percent aqueous sloution of pigskin gelatin having its iso-electric point at pH 8. The emulsion, when reduced to the desired drop-size, has its pH adjusted, if necessary, to 9, or above, with a 5 percent aqueous solution of sodium hydroxide. To this emulsion is added 9 parts, by weight, of an 11 percent aqueous sol of gum arabic, which sol had previously been adjusted to pH 9, or above, with the equivalent sodium hydroxide solution. The emulsion mixture then is diluted with Water to a total volume of 375 milliliters, and phase separation of the gelatin and gum arabic molecules as complex entitles is induced by lowering the pH, with a 15 percent aqueous solution of acetic acid, to 4.6. All the foregoing steps are performed at a temperature of about 50 degrees centigrade, with constant agitation. The capsules are now formed, but the capsule walls are in a liquid condition, ready to be solidified or made rigid, which is accomplished, as the next step, by reducing the temperature of the agitated dispersion medium and capsules to about 14 degrees centigrade. To the resulting dispersion of capsules with solid walls is added 0.5 part, by weight, of a 25 percent aqueous solution of glutaraldehyde to harden the capsules, which hardening is completed in a few hours. The residual polymer-poor aqueous medium of the dispersion may be reduced in quantity or eliminated by any convenient means, such as evaporation, decantation, filtering, or centrifuging, to the condition in which it is desired to use the capsules.

The second example consists of a method for producing capsules having the gas-producing substance in both the core materials of the capsules and the wall mat rials of the capsules, and these gas-producing substances may be of one kind in the capsular core materials and of another kind in the capsule wall material. The method of the first example may be modified to obtain this result. Stipulating that the Celogen has been dispersed in the polyethyl benzene, which thereafter is dispersed in the aqueous medium, followed by the additions of the gelatin sol and the gum arabic sol, as previously set forth, and that phase separation has been induced, then, just after the phase separation has started to deposit on the polyethyl benzene droplets containing the Celogen, and beiore polymer deposit on the droplets has ceased, there are added to the system, and stirred in, particles of azocarbonamide, the total weight of the gasproducing agents not to exceed about 15 percent, by weight, of the polyethyl benzene to prevent possible interference with the polymer deposition thereon.

As a third example of the making of heat-rupturable liquid-solvent-containing capsules, 20 grams of Celogen is dispersed in 40 grams of Water, using a wetting agent if necessary to obtain good dispersion. Next, an emulsion of cc. of polyethyl benzene in grams of an 11 percent, by Weight, aqueous gelatin sol is prepared. When the size of the polyethyl benzene dropshas been reduced to 5 microns or less, the Water-Celogen dispersion is mixed therewith. Next, 180 grams of an 11 percent, by weight, aqueous gum arabic sol is stirred into the mixture, all the components being at 50 degrees centigrade. Water is added to bring the total volume of the system to 1800 cc., and thereafter phase separation is induced by causing complex entities of the gelatin and gum arabic components to form, by adjusting the pH of the system to 4.6, whereupon the complex entities of gelatin and gum arabic sols, which are relatively rich in polymer material compared to the equilibrium liquid, collect onto the polyethyl benzene droplets and the Celogen particles as seed points, where they coalesce into liquid walls wrapped around the droplets and included particles. The system then is cooled to 14- degrees centigrade to set the liquid Walls to a firm condition, and the completed capsules are recovered and used, as described, for coating the base web. Upon the application of heat after the image has been fixed, the remaining capsule walls amen ts disintegrate, releasing the solvent to dissolve the particles of colorless dye former adjacent thereto, which solvent, when it evaporates, leaves the dye former in solid colorless inert form.

The method of making record material, diagrammatically shown in FIG. 1, having a coating of liquid-solventcontaining microscopic rupturable capsules interspersed in profusion with microscopic particles of photo-sensitive colorless dye former which responds in liquid solution resulting locally by reason of rupture of the capsules and release of the solvent having now been described, the method of the use of such will follow.

In the simplest use of the record material, it is subjected to letter-press typing, without ink on the type, as with a ribbonless typewriter, or by an uninked printing array in a printing press. The capsules are ruptured in conformity with the type characters, leaving a latent image in colorless liquid solution of the dye former, as shown in FIG. 2. Before the solvent evaporates, the record material sheet bearing the liquid latent image is subjected to ultra-violet light (under 4000 A.) to develop color in the latent image, as shown in FIG. 3. The process may be stopped at this point, but the unbroken capsules still may be broken later and developed in the same manner to make additional areas responsive to ultra-violet light. To prevent this later action, the sheet, after first being developed, is passed through rollers to break all the rest of the unruptured capsules, and the released solvent is allowed to evaporate without developing color in the dye former in contact therewith by protecting it from light predominating in ultra-violet components until it dries into an inert solid condition. It is a characteristic of the colored dye solution that it will revert to the colorless form when subjected to light predominating in wave lengths in the region of the spectrum from green through infra-red, and such reversing light should be avoided until the dissolved and colored dye is dried to a solid, unless erasure of part or all of the image is desired, such erasure being made by selectively subjecting the wet colored image to erasing light. The optional calendering step is shown in FIG. 4.

In a second method of using the prepared sheet of FIG. 1, it is subjected to a squeeze pressure by an embossing machine, the capsules being ruptured by the combined pressure and rubbing action which occurs. The image on the portions forming the relief of the embossed image or the intaglio image portions are subjected to capsule rupture, the resulting latent image being developed by light and fixed by evaporation and by calendering, if the latter is desired.

If the novel capsule-bearing sheet has not only a photoresponsive liquid in the capsules, but a gas-producing material in said liquid or in the walls of the capsules, or in both, such gas-producing substance forming a gas when heated, a latent image may be formed on the sheet by hot type, by a hot stylus, by a hot embossing die, or by heat rays which are directed thereagainst, the applied heat mak ing the capsules break to release the solvent, thus forming the latent image in photo-responsive liquid solution form, which may be developed by ultra-violet light. If the light contains components that furnish both the image-developing light and the heat necessary to rupture the capsules, the image may be formed without the separate performance of the ultra-violet radiation step. In one form of the invention, it is contemplated to apply heat to the novel sheet according to an image, such being accomplished by use of a master sheet having the image to be copied delineated in heat-absorbent and heat-non-absorbent areas, such as typified by a master letter typewritten upon white paper with black ink. This master letter, if translucent in the unprinted areas, is placed against the capsular coated surface of the novel record sheet coated with capsules containing not only the solvent for the photoresponsive dye former, but also the gas-producing substance. Light having a large component of heat rays 6 then may be passed through the two sheets, the black type absorbing the heat, thus bursting the capsules in contact therewith. The resulting latent image may be developed by ultra-violet light in the described manner, followed by fixing the non-colored areas of the sheet, if desired, by pressure, followed by evaporation of the solvent.

In another use of the novel sheet having the heatrupturable capsules coated thereon, and the base web passing heat radiation, the sheet is placed with the uncoated side against a master sheet to be copied, said master sheet having the image to be copied thereon in black, or dark, heat-absorbing areas, and heat radiation is applied through the capsule coating, which. is heated by reason of the dark heat-absorbing image on the master sheet, according to the image on the master sheet, thus rupturing the capsules according to the said image on the master sheet. The latent image formed by the ruptured capsules then may be developed by ultra-violet light and fixed, as has been described. Any other method of controlling the application of heat to the novel sheet by means of a master image may be used instead of those methods particularly described, as the dark master image to be copied may be used either for its light absorption and consequent diiferential heating with respect to the rest of the master sheet, or for its effect in preventing the transmission of heat radiation therethrough.

The invention in its best forms, which are not to be deemed to limit it, having thus been disclosed, the invention is claimed as follows.

What is claimed is:

1. A base record sheet having thereon a coating consisting of a profuse interspersion of solid particles of substantially colorless organic dye former material, which material when in liquid solution turns to a colored state when subjected to ultra-violet light, and rupturable capsules containing, as a nucleus material, a liquid so vent for the solid particles of material, the particles and the capsules being of such small size that their indivitual identity cannot be resolved by the unaided eye, the capsules each containing an additional substance which produces gas to rupture such capsules when heated, releasing the solvent to dissolve the solid particles in contiguity therewith, thus rendering any selected areas of the sheet which have been heated, with accompanying capsule rupture, sensitive to ultra-violet light, the sosensitized areas of the sheet rendering a colored image corresponding to the areas where capsules have been ruptured, when the sheet as a whole is subjected to ultraviolet light.

2. The record sheet of claim 1 in which the solvent is volatile whereby upon the vaporization and escape of the solvent from the colored areas such areas are fixed in the colored state.

3. The method of recording on a record sheet having a base web coated with a profuse interspersion of solid particles of substantially colorless organic dye former material, which material when in liquid solution turns to a colored state when subjected to ultra-violet light, and rupturable capsules each containing as a nucleus material a volatile liquid solvent for the particles of solid material, the capsules and the particles being of such small size that their individual identity cannot be resolved by the unaided eye, including the steps of selectively rupturing capsules in areas of the coated sheet where it is desired that there should be visible color to form an image, thus releasing the solvent in those areas; and subjecting the sheet to ultra-violet light, whereby color will be developed in the particles contiguous to the ruptured capsules and which have been dissolved by the released solvent.

4. The method of claim 3 in which the selected areas of the sheet are subjected to a type-impression to rupture the capsules.

5. The method of claim 3 in which the selected areas of the sheet are subjected to the impression of a stylus drawn thereacross to rupture the capsules.

6. The method of claim 3 in which the selected areas have been subjected to the squeeze of an embossing die to rupture the capsules.

7. The method of claim 3 in which there has been provided in the materials of the capsule a substance which normally is not in a gaseous state but which turns to a gas when heated, and in which method the capsules in the areas to be colored are ruptured by heat applied thereto.

8. The method of claim 7 in which the heat is applied by hot type.

9. The method of claim 7 in which the heat is applied by a ho: stylus.

10. The method of claim 7 in which the heat is applied by heat radiation projected according to the desired image.

11. The method of claim 3 in which the whole sheet is calendered after the image has been developed by ultra-violet light to rupture the capsules in uncolored areas of the sheet, thus rendering them inert to ultraviolet light after the released solvent has evaporated.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A BASE RECORD SHEET HAVING THEREON A COATING CONSISTING OF A PROFUSE INTERSPERSION OF SOLID PARTICLES OF SUBSTANTIALLY COLORLESS ORGANIC DYE FORMER MATERIAL, WHICH MATERIAL WHEN IN LIQUID SOLUTION TURNS TO A COLORED STATE WHEN SUBJECTED TO ULTRA-VIOLET LIGHT, AND RUPTURABLE CAPSULES CONTAINING, AS A NUCLEUS MATERIAL, A LIQUID SOLVENT FOR THE SOLID PARTICLES OF MATERIAL, THE PARTICLES AND THE CAPSULES BEING OF SUCH SMALL SIZE THAT THEIR IDIVIDUAL IDENTITY CANNOT BE RESOLVED BY THE UNAIDED EYE, THE CAPSULES EACH CONTAINING AN ADDITIONAL SUBSTANCE WHICH PRODUCES GAS TO RUPTURE SUCH CAPSULES WHEN HEATED, RE- 